1. The Field of the Invention
The present invention relates to the manufacture of semiconductor devices. More particularly, the present invention is directed to methods for controlled, selective, polysilicon etching useful in the fabrication of semiconductor devices employing polysilicon.
2. The Relevant Technology
Polysilicon is extensively employed in the fabrication of silicon based semiconductor devices. Traditionally, wet etchants for polysilicon are the same as, or very similar to, wet etchants used for single crystal silicon. Wet etchants for polysilicon thus generally include hydrofluoric and nitric acids in solution with water or acetic acid. Such traditional polysilicon etchants etch polysilicon quite rapidly, as fast as 3000 Angstroms per minute, but cannot be significantly diluted without losing virtually all etching ability. Traditional polysilicon etchants also tend to produce non-uniform etch rates over the surface of a wafer, possibly because of autocatalysis, or because the reaction involved proceeds faster at high temperatures and is exothermic so that the reaction speed is increased by the heat produced by the reaction itself. Because of these characteristics, traditional polysilicon wet etchants are useful only where an entire layer of polysilicon and/or silicon must be removed. For carefully controlled partial etching of polysilicon layers, new etching technology is needed.
In the continuing quest for increased miniaturization of memory circuits, the area of a chip occupied by a capacitor in DRAM circuits, and in circuits of similar technologies, must be decreased. But capacitance is a function of capacitor plate area, and capacitance must remain large enough to provide a clear, reliable signal at each refresh cycle, or else memory integrity is lost. Ways to increase capacitance of capacitors in DRAM and related circuits are thus needed.